Ultrastructural morphometric studies on regeneration of the lateral sural cutaneous nerve in the white rat after transection of the sciatic nerve.

Abstract

The lateral sural cutaneous nerves of 49 Sprague-Dawley rats 7-76 weeks of age were examined morphometrically in single transverse sections using electron microscopy. The following variables were estimated: the relative proportions of collagen-occupied and collagen-free areas of the extracellular compartment of the endoneurial space, the number and the diameters of axons, the number of myelin lamellae, and the number of different kinds of cell nuclei. The nerve contained on the average 2600 axons of which about 2200 (85%) were unmyelinated. The different variables were computed with regard to the animal-to-animal, side-to-side, and age variations. From these data normal reference diagrams based on the 95% prediction intervals for individual observations were constructed. Animal-to-animal and side-to-side variations were of about the same magnitude except in cases where the variation was age-dependent. Prediction intervals for individual observations that were +/- 50-70% of the mean value were found for the numbers of different types of Schwann cell nuclei. The intervals for the number and mean diameters of unmyelinated axons and myelinated fibres was +/- 20-30%. The g-value showed the narrowest interval +/- 10%. Age-related variation was found for the transverse section area of the nerve, axon diameters, and the number of myelin sheath lamellae. The application of normal values as a reference system to experimental data is discussed.